Several issues cloud the matter.
You said "sketch or render" in your posting.
You did NOT say line drawing.
Yes, line drawings should be rastered to 1200dpi, but these aren't renderings, they would be rastered from vector output. No greyscale.
First: You can't render more than 4048x4048 pixels in LightWorks.
Big renderings are done in Artlantis.
Second: If you make more than 300 dpi for a full color image it is probably a waste unless they are going for specialty printing on synthetic stock. Your guys will probably use a line screen of 150lpi and 2x is the ratio. Is this an art book?
As for high resolution sketch rendering or photo-realistic rendering, the true limit is not the rendering engine but texture resolution. The "lines" in a sketch rendering are actually small TIF files - they never highly resolve [see: Visualization>SketchTextures> 01_Crayon_AD for an example of resolution limits]. At a certain point, the sketch lines themselves reveal pixels.
If you need larger sketch renderings, use tools like Genuine Fractals or Sharpener Pro to improve apparent sharpness.
But Junior is in the ballpark with 150dpi for inkjet output.
As for rendering in LightWorks above 2000 pixels of a typical building, standard Archicad texture maps begin to blur and reveal chromatic aberration. You get nice sharp edges with a blurry mess inside. Very amatoor.
Dwight Atkinson